The present invention relates generally to high voltage feedthrough assemblies and more particularly to an insulator for use in such assemblies.
Feedthrough assemblies are used to conduct high voltages into the interior of enclosed and grounded chambers. For example, such assemblies can be used to connect a high voltage (50 kilovolts or more) to an electrostatic quadrupole focusing unit in a fusion energy accelerating system.
Typically, such an assembly uses a conductor rod which extends from outside a grounded housing through an opening in the housing, the conductor rod having a terminal outside of the housing to which a source of high voltage may be connected. An insulator extends between the conductor and the housing to support the conductor rod in spaced relation to the housing opening, to seal the interior of the housing from the exterior thereof and to provide an electrical insulation capable of withstanding breakdown under the stresses of the high voltage electric field created between the conductor and housing.
Commercial high voltage insulators are generally made of ceramic material, such as zircon or steatite, and are designed to withstand a high voltage along their external surfaces. The design considerations for a feedthrough insulator are quite different, because the voltage gradient is from the center rod or conductor through the insulator to the insulator support, the latter being usually at ground potential.
Hollow, cylindrical ceramic insulators have been tested and found unsuitable for high voltage feedthrough. In particular, it has been found that field emission from the center rod results in a spark breakdown through the ceramic to the metal support, burning a hole through the insulator and causing pitting of the rod.